This invention relates to spirit levels and is particularly directed to spirit levels which are uniquely suited to mass production and which provide unique protection of the bubble tube against contamination by dirt, grease or the like.
Spirit levels have long been useful in carpentry and construction work for assuring that a surface is truly horizontal or vertical. Traditionally, spirit levels have comprised one or more slightly arcuate tubes substantially filled with fluid but containing an air bubble. By mounting these "bubble tubes" on an elongated bar, with the curve lying convexly with respect to the surface of the bar, the air bubble will tend to move toward the center or high point of the tube and, by calibrating the device on a known level surface and providing sight lines at the center or opposite edges of the bubble, the device can be used subsequently to measure the levelness of an unknown surface. Customarily, one or more adjustment screws are provided to permit slight movement of the bubble tube during calibration. Unfortunately, spirit levels are frequently used in carpentry or construction areas where there is considerable dust, sawdust, grease and the like which can intrude into the region about the bubble tube and can interfere with the positioning and calibration of the bubble tube. Furthermore, the mounting, positioning and calibration of the bubble tube on the bar has, in the past, required a considerable amount of manual labor, which has restricted or prevented the mass production of spirit levels and, consequently, has caused them to be relatively expensive.
A search in the U.S. Patent Office has revealed the following patents:
______________________________________ U. S. Pat. No. Inventor Issued ______________________________________ 353,846 G. Cook Dec. 7, 1886 421,786 J. A. Traut Feb. 18, 1890 465,882 C. E. Peterson Dec. 29, 1891 1,017,646 G. Broadmore Feb. 20, 1912 1,515,239 H. J. Cook Nov. 11, 1924 1,815,949 O. Marischal July 28, 1931 2,101,077 A. Langsner Dec. 7, 1937 2,301,769 F. A. Babcock Nov. 10, 1942 2,557,291 R. T. Hubbard June 19, 1951 2,567,553 C. P. Davey Sept. 11, 1951 4,299,035 S. Stauber Nov. 10, 1981 4,542,592 R. E. Hopkins Sept. 24, 1985 ______________________________________
The patents to Broadmore and G. Cook each disclose spirit levels wherein the bubble tube is protected from invasion by dirt, but each require considerable manual labor to assemble and calibrate. The remaining patents each disclose spirit levels in which the bubble tube and the adjusting mechanism therefor are exposed and susceptible to invasion by dirt and dust. Thus, none of the prior art devices are entirely satisfactory.
These disadvantages of prior art spirit levels are overcome with the present invention and a spirit level is provided which totally precludes intrusion of dirt, dust or the like into the region of the bubble tube or its adjustment mechanism, yet which requires minimal manual labor for assembly and calibration and, hence, is particularly well suited to mass production.
The advantages of the present invention are preferably attained by providing a spirit level formed of a hollow, rectangular bar of extruded material having end caps for closing the ends thereof and formed with recesses formed in said bar for receiving bubble tubes; together with a sealed capsule, mountable adjacent said recesses, containing a bubble tube and adjustment mechanism therefor. Because the bubble tube and adjustment mechanism are sealed within the capsule, invasion by dirt or dust is virtually precluded. Moreover, should the capsule or its contents become damaged in any way, they can readily be removed and replaced. Also, the capsules can be produced independently, in any desired quantity, and can be assembled quickly and easily with the extruded bar and end caps to permit mass production of spirit levels embodying the present invention.
Accordingly, it is an object of the present invention to provide improved spirit levels.
Another object of the present invention is to provide improved spirit levels which virtually preclude invasion of the region about the bubble tube or its adjusting mechanism.
An additional object of the present invention is to provide spirit levels which are uniquely adapted to mass production.
A further object of the present invention is to provide spirit levels wherein the bubble tube can be replaced quickly and easily.
A specific object of the present invention is to provide a spirit level comprising a hollow rectangular bar of extruded material formed with at least one recess for receiving a bubble tube and having end caps for closing the ends of said bar; together with a sealed capsule, mountable adjacent said recess, containing a bubble tube and adjustment mechanism therefor.
These and other objects and features of the present invention will be apparent from the following detailed description, taken with reference to the figures of the accompanying drawing.